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Paul L · 05-02-2017, 00:34

It's a multiplexer then - even if someone wants to call it a merger.

barnakiel · 05-02-2017, 06:28

You also make a merging operation when you have e.g. 3 wind units that do not work on the fall back basis.

b.

tanglewood · 05-02-2017, 10:25

Quote:

Originally Posted by gmartin83

No, notice I mentionned NMEA0183 phrases, not NMEA200 pgn.
See B&G network, please.

Who builds such a thing?

gmartin83 · 05-02-2017, 12:32

As far as I know, there is at least one German company, if you are interested in, I could look for their coordinates. I think to develop one for my own needs.

tanglewood · 05-02-2017, 22:54

Quote:

Originally Posted by gmartin83

As far as I know, there is at least one German company, if you are interested in, I could look for their coordinates. I think to develop one for my own needs.

Yes, I'd be interested in the company name and/or product name.

I suspect either:

1) We are all talking about the same thing, but confusing each other with terminology.

OR

2) You and the German company have figured out some magic that none of the rest of us understand.

OR

3) You don't really understand this, and don't know that you don't understand it.

I hope for #1, but fear it's #3

gmartin83 · 06-02-2017, 01:03

#2, I'm talking about a well-known process that has nothing magical.
Unfortunately, often people are reluctant to accept unusual ideas.
Knowing that, at least, one person will read it, I will prepare a description of this process and send it tomorrow.

tanglewood · 06-02-2017, 09:47

Quote:

Originally Posted by gmartin83

#2, I'm talking about a well-known process that has nothing magical.
Unfortunately, often people are reluctant to accept unusual ideas.
Knowing that, at least, one person will read it, I will prepare a description of this process and send it tomorrow.

I look forward to reading it, as I'm sure do others.

barnakiel · 07-02-2017, 05:54

I think one scenario when a multiplexer box could be called a merger box is when it e.g. averages equivalent same sentences coming from multiple sensors. Vide NKE wind multiplexer box (3 wind inputs, one, averaged wind data sentence out).

Call it a 'smart, dedicated multiplexer'.

Looking forward to aforementioned info on the merger box too.

b.

gmartin83 · 12-02-2017, 00:47

Hello,

Please find attached a description of different communication systems.

tanglewood · 12-02-2017, 01:15

Quote:

Originally Posted by gmartin83

Hello,

Please find attached a description of different communication systems.

OK, thanks. Like you said earlier, it's nothing new. But it's not 0183 or how RS422 works. What you have described is how RS485 works, and the whole collision detection concept goes back to the first 1mb ethernet. It's kind of how NMEA 2000 works, though that's more of a priority access algorithm.

So yes, you could build such a thing, and many people have over the years. But it's contrary to how NMEA 0183 works, and none of the RS422 UARTs work that way either.

And the existing "multiplexer" approach works just fine, though it's multiplexing at the datalink layer by queuing whole messages that have been buffered from various inputs.

Sandero · 12-02-2017, 02:50

For NMEA 0184...I thought... correct me if I am wrong... you can have up to 4 listeners connected to one terminal. My understanding was that the current was not able to support more than that. I don't where I got this idea... And it has nothing to do with several talkers connected together... to one or more listeners... that would require multiplexing I believe.

barnakiel · 12-02-2017, 05:45

OK. The general idea is the same only the use of words is the opposite: multiplexer for one way comm (what I call a combo box - e.g. NKE wind sensor combo box = ONE WAY com) and the other device is here called a Merge box (which I actually call the opposite = a multiplexer, like the Brooks box that is called a multiplexer by Brooks = TWO way com).

Just how we use the words but otherwise the same ideas.

I think it could be easier just call them 'one-way' or 'two way' and then say either Merge box or Multiplexer. Same same. Only the 'talk-back' ability being the difference.

??? yes no? something in between?

BTW How much one can split the signal (232, 422, etc) depends on talker and listener electrical parameters. I have seen splitting in two always works. Splitting more ways at a point the listeners stop reading the input. Hardware dependent.

b.

barnakiel · 12-02-2017, 05:51

Back to OP question.

If one wants to connect many nmea talkers onto one nmea listener, one needs either separate nmea inputs on the listener or else the talkers must be combined via a 'box' - before being attached to a single listener terminal.

These boxes may talk one way or be bi-dirrectional.

This is to say we are back at square A1.

b.

tanglewood · 12-02-2017, 11:09

Quote:

Originally Posted by barnakiel

OK. The general idea is the same only the use of words is the opposite: multiplexer for one way comm (what I call a combo box - e.g. NKE wind sensor combo box = ONE WAY com) and the other device is here called a Merge box (which I actually call the opposite = a multiplexer, like the Brooks box that is called a multiplexer by Brooks = TWO way com).

Just how we use the words but otherwise the same ideas.

I think it could be easier just call them 'one-way' or 'two way' and then say either Merge box or Multiplexer. Same same. Only the 'talk-back' ability being the difference.

??? yes no? something in between?

BTW How much one can split the signal (232, 422, etc) depends on talker and listener electrical parameters. I have seen splitting in two always works. Splitting more ways at a point the listeners stop reading the input. Hardware dependent.

b.

I think there is a little more to it than that. Gerard's drawings show multiple devices both talking and listening on the same bus. For that to work, all the talkers need to be electrically and logically (protocols) capable of doing that. NMEA 0183, and RS422 (what it's built on) supports neither of those capabilities.

RS422 electrical outputs are always active. They are not tri-state or open collector. This means that every talker is always driving the wires to be a "one" or "zero" voltage, even when not actively talking. If another talker tries to send a sentence it will be trying to drive the wires to different voltages than the other talker. For multi talkers to work, each must completely release the bus when idle so another talker can drive it without opposition. RS422 simply doesn't support that.

And even if two talkers could co-exist electrically, none of the logic exists in any 0183 products to implement the access protocol described in the paper. And all talkers would need to follow the same protocol.

In marine electronics, there are two widely used communications interfaces that so support multiple talkers on the same bus. They are NMEA 2000 using Canbus technology, and Ethernet.